1. First, the event code in Page_Load of the aspx file of the background verification code:
using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.UI; using System.Web.UI.WebControls; using System.Drawing; namespace 学生在线考试系统 { public partial class AjaxAutoCode : System.Web.UI.Page { //验证数字 public string authcode = string.Empty; protected void Page_Load(object sender, EventArgs e) { #region 第一种产生验证码的方法 Random random = new Random(); authcode = random.Next(1111, 9999).ToString(); //构造图片 Bitmap image = new Bitmap(authcode.Length * 12, 25); //创建画布 Graphics g = Graphics.FromImage(image); try { g.Clear(Color.White); for (int i = 0; i < 25; i++) { int x1 = random.Next(image.Width); int x2 = random.Next(image.Width); int y1 = random.Next(image.Height); int y2 = random.Next(image.Height); //链接两点的线条 g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2); } Font font = new Font("Arial", 12, FontStyle.Bold | FontStyle.Italic); System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush( new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkBlue, 1.2f, true); g.DrawString(authcode, font, brush, 2, 2); //画图片的前景噪点 for (int i = 0; i < 100; i++) { int x = random.Next(image.Width); int y = random.Next(image.Height); image.SetPixel(x, y, Color.FromArgb(random.Next())); } g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1); System.IO.MemoryStream ms = new System.IO.MemoryStream(); image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif); ms.WriteTo(this.Response.OutputStream); ms.Close(); this.Response.ContentType = "image/gif"; } finally { image.Dispose(); g.Dispose(); } #endregion } } }
2. Secondly, define a JS function on the page that displays the verification code
function fGetCode() { document.getElementById("getcode").src="Default2.aspx?"+Math.random(); }
3. Then edit the front page aspx, the following is the code snippet of the front page
<label>验证码</label> <asp:TextBox ID="txt_checkCode" runat="server" Width="178px"></asp:TextBox> <img src="/static/imghwm/default1.png" data-src="Default2.aspx" class="lazy" alt="看不清楚?" id="getcode"/> <a href="javascript:fGetCode()">更换验证码</a>
For more asp.net ajax implementation of non-refresh verification code related articles, please pay attention to the PHP Chinese website!

The char array stores character sequences in C language and is declared as char array_name[size]. The access element is passed through the subscript operator, and the element ends with the null terminator '\0', which represents the end point of the string. The C language provides a variety of string manipulation functions, such as strlen(), strcpy(), strcat() and strcmp().

The usage methods of symbols in C language cover arithmetic, assignment, conditions, logic, bit operators, etc. Arithmetic operators are used for basic mathematical operations, assignment operators are used for assignment and addition, subtraction, multiplication and division assignment, condition operators are used for different operations according to conditions, logical operators are used for logical operations, bit operators are used for bit-level operations, and special constants are used to represent null pointers, end-of-file markers, and non-numeric values.

In C, the char type is used in strings: 1. Store a single character; 2. Use an array to represent a string and end with a null terminator; 3. Operate through a string operation function; 4. Read or output a string from the keyboard.

In C language, special characters are processed through escape sequences, such as: \n represents line breaks. \t means tab character. Use escape sequences or character constants to represent special characters, such as char c = '\n'. Note that the backslash needs to be escaped twice. Different platforms and compilers may have different escape sequences, please consult the documentation.

A strategy to avoid errors caused by default in C switch statements: use enums instead of constants, limiting the value of the case statement to a valid member of the enum. Use fallthrough in the last case statement to let the program continue to execute the following code. For switch statements without fallthrough, always add a default statement for error handling or provide default behavior.

There is no built-in sum function in C language, so it needs to be written by yourself. Sum can be achieved by traversing the array and accumulating elements: Loop version: Sum is calculated using for loop and array length. Pointer version: Use pointers to point to array elements, and efficient summing is achieved through self-increment pointers. Dynamically allocate array version: Dynamically allocate arrays and manage memory yourself, ensuring that allocated memory is freed to prevent memory leaks.

In C language, char type conversion can be directly converted to another type by: casting: using casting characters. Automatic type conversion: When one type of data can accommodate another type of value, the compiler automatically converts it.

The core concepts of .NET asynchronous programming, LINQ and EFCore are: 1. Asynchronous programming improves application responsiveness through async and await; 2. LINQ simplifies data query through unified syntax; 3. EFCore simplifies database operations through ORM.


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